When jetting a fluid onto a heated surface it is highly desirable for 100% of the fluid to vaporize so that liquid is not discharged from the vaporizing device. The problem lies in that the vaporizing heater must be small enough to heat up extremely quickly, but yet has enough surface area to catch all fluid and fluid droplets that are being ejected onto the heating element. A typical metal foil heating element has a smooth surface with minimal liquid/heater interface which is due to a low surface roughness of the heating element surface. Accordingly, some of the fluid droplets impinging on the surface of the heating element will be scattered or fluid droplets will be ejected from the heating element if a significant layer of fluid already exists on the surface of the heating element when new droplets arrive. Thus, instead of only vapor being discharged from the vaporization device, liquid droplets may be entrained in the vapor and discharged from the vaporization device. In some applications, the discharge of liquid is not only undesirable, but may be detrimental to the user. Also, unvaporized fluid may build up inside the vaporization device and thus degrade the operation of the device.
In order to avoid the discharge of liquid droplets from a vaporization device, the stream of fluid ejected onto the surface of the heating element must be efficiently captured by the heating element, spread out over the surface of the heating element, and completely vaporized at approximately the same rate as the fluid arrives on the surface of the heating element in order to avoid liquid accumulation on the surface of the heating element.
In view of the foregoing, embodiments of the disclosure provide a heating element for a vaporizing device, a vaporizing device containing the heating element, and a method for vaporizing fluid ejected by an ejection head. The heating element includes a conductive material deposited onto an insulative substrate, a protective layer deposited onto the conductive layer, and a porous layer having a porosity of at least about 50% deposited onto the protective layer. The heating element has an effective surface area (ESA) for fluid vaporization that is greater than a planar surface area defined by dimensions of the heating element so that a fluid contact surface of the heating element is greater than the planar surface area of the heating element.
In one embodiment, the heating element has a rectangular shape. Accordingly, the effective surface area (ESA) of the heating element is defined by the equation ESA>L×W, wherein L is a length of the heating element and W is a width of the heating element that is exposed to a vaporizing fluid.
In another embodiment, the heating element has a circular shape. Accordingly, the effective surface area (ESA) of the heating element is defined by the equation ESA>Π×R2 wherein R is a radius of the heating element that is exposed to a vaporizing fluid.
Another embodiment of the disclosure provides a vaporizing device that includes a housing body, a mouthpiece attached to the housing body, and a heating element disposed adjacent to the mouthpiece for vaporizing fluid ejected from an ejection head. The heating element has a conductive material deposited onto an insulative substrate, a protective layer deposited onto the conductive layer, and a porous layer having a porosity of at least about 50% deposited onto the protective layer.
A further embodiment of the disclosure provides a method for vaporizing a fluid ejected by an ejection head so that substantially all of the fluid ejected by the ejection head is vaporized. The method includes providing a vaporization device having an ejection head and a vaporizing heater element adjacent to the ejection head; ejecting fluid onto the heater element; activating the heating element during fluid ejection; and vaporizing substantially all of the fluid using the heating element. The heating element has a conductive material deposited on an insulative substrate, a protective layer deposited on the conductive layer, and a porous layer having a porosity of at least about 50% deposited onto the protective layer.
In some embodiments, the porous layer has a grit blasted surface texture that provides the effective surface area (ESA) thereof. In other embodiments, the porous layer is a grit blasted ceramic material.
In another embodiment, the porous layer is a laser etched ceramic layer.
In yet another embodiment, the porous layer is deposited as a coarse glass frit that is sintered onto a surface of the heating element.
In some embodiments, the porous layer has a thickness ranging from about 0.5 millimeters (mm) to about 3 mm. In other embodiments the porous layer has a thickness ranging from about 1 mm to about 2 mm.
In some embodiments, the insulative substrate, conductive layer and protective layer have a combined thickness ranging from about 4 millimeters (mm) to about 1 centimeter (cm)
In some embodiments, the porous layer has a porosity ranging from about 50% to about 95%.
In some embodiments, the conductive layer is a screen printed conductive layer deposited onto a ceramic substrate.